Methane is a prevalent greenhouse gas that contributes to global warming. While synthetically it is difficult to chemically convert methane to less environmentally harmful substances, methanotrophic bacteria have developed an efficient way to metabolize methane. In the first step of the process, methanotrophs use a copper dependent enzyme complex called particulate methane monooxygenase (pMMO) to convert methane to methanol, but precisely how this occurs biochemically and how pMMO may be regulated are not well understood. The primary goal of this proposal is to characterize a protein called pmoD that is also likely involved in methane conversion and may somehow regulate pMMO. In one component of this work the phenotype of pmoD will be studied using a pmoD knockout strain. A second aspect of the work will focus on structural, biochemical, and spectroscopic characterization of pmoD. The third aim addresses the function of pmoD by determining whether it can interact with other proteins involved in copper metabolism and methane conversion and whether it can regulate these processes. Together, this combination of in'vivo studies, structural characterization, and biochemical analysis is expected to provide a comprehensive description of pmoD and its roles in methane metabolism and copper regulation. The insights gained from these studies have the potential to greatly enhance the current understanding of biological methane oxidation. Biochemical analysis is expected to provide a comprehensive description of pmoD and its roles in methane metabolism and copper regulation. The insights gained from these studies have the potential to greatly enhance the current understanding of biological methane oxidation.